1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) device, and more particularly to an OLED device capable of adjusting luminance.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 illustrates a circuit diagram of controlling a conventional OLED 100. As illustrated in FIG. 1, the conventional OLED device 100 includes a reference current source IREF, two transistors Q1 and Q2, an OLED equivalent module 110, a bias source VH, and a variable resistor VR1. The OLED equivalent module 110 includes an OLED D1, an equivalent capacitor C1, two resistors R1 and R2. Luminance of the OLED D1 is determined by current that flows through identity, therefore in order to change the luminance of the OLED D1, the current that flows through identity has to be changed. As illustrated in FIG. 1, the transistors Q1 and Q2 is connected as a current mirror, which duplicates the reference current IREF to the transistor Q2 such that the current outputted by the transistor Q2 is the same as IREF. The current IREF outputted by the transistor Q2 is split into two currents I1 and I2 after passing through parallel circuits formed by the OLED equivalent module 110 and the variable resistor VR1, thus the current that flowed through the OLED equivalent module 110 is I1, as the addition of currents I1 and I2 equals to the current IREF, then the value of the current I1 can be changed by changing the value of the current I2. Therefore, a resistance value of the variable resistor VR1 can be utilized to change the value of the current I2, in doing so the value of the current I1 passing through the OLED equivalent module 110 is also changed; hence the objective of changing the luminance of the OLED equivalent module 110 is reached.
But there are a few problems in the above-mentioned prior art in controlling the luminance of the OLED device. First, in the manufacturing process, it is not easy to fit the whole devices of the above-mentioned into a same chip as the variable resistor takes up a significant surface area. Hence this method is not suitable or compliant for the current trend of producing smaller chipsets. Second, if the variable resistor is further coupled to the external portion of the OLED in a discrete manner, the resistance value of the variable resistor may shift and fix at a predetermined value difficulty. Lastly, during manufacturing, each variable resistor that controls the OLED device needs to be adjusted so that the luminance of the OLED can be uniform, thus this method is unable to effectively control the OLED.